There are a few zooms within Shotcut. There is a filter zoom and a preview zoom. Are you referring to Zoom within the filter Size, Position & Rotate?
As with other video editors, the first important step to Shotcut is to set the correct Video Mode (Resolution/FPS) for your project.
What does Shotcut show in the Properties window for your video clip? Does the resolution match up with the Video Mode?
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Properties → Select clip
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Properties → Click on “Output”
In your project, do your resolution/fps match?